Electric energy meters are designed to account energy under sinusoidal and nonsinusoidal conditions, because both, old and new standards for energy meters require testing their accuracy under different conditions. The latest EN 50470 standard increases the range of meter testing under nonsinusoidal conditions, introducing new shapes of test signals such as the phase fired waveform or the burst fired waveform. This paper discusses calibration problems of electronic revenue energy meters for direct connection and for connection through current transformers, and it proposes a new calibration procedure which reproduces normal operating conditions better: three-phase configurations of measurement systems, load range during meter testing or shapes of test signals. Recently, modern Electrical Power Standards, also known as Power Calibrators, enable automatic testing of various types of electrical devices, including electricity meters in their normal operating conditions. This article presents examples of single and multi position fully automatic test systems, which employ Power/Energy Calibrator from Poland as the precision source with programmed waveforms of three phase voltages up to 560 V and currents up to 120 A conforming to EN 50470, or with random waveforms generated by PC software random wave generator. Measurement uncertainty of the energy meters under different nonsinusoidal conditions using a test system with reference to accuracy of the power calibrator or to the reference meter, are discussed. Comparative analysis of test results for different shapes of voltage and current signals is presented in the conclusions of this paper.